Conventional methods for adding water-insoluble photographic additives to a silver halide photographic emulsion include the following processes (1) dissolving a photographic additive or additives in an organic solvent such as methanol and then adding the resulting solution to a silver halide emulsion as described, for example, in JP-B-50-40659 (The term "JP-B" as used herein means an "examined Japanese patent publication"), U.S. Pat. No. 3,788,857, JP-A-50-11419 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"), U.S. Pat. No. 3,660,101, and JP-B-49-46416; (2) dissolving a water-insoluble photographic additive or additives in an organic solvent, mixing the resulting solution with water, then removing said organic solvent to form a dispersion in water as described, for example, in JP-A-49-128725; (3) solubilizing a water-insoluble photographic additive or additives, and adding the solubilized solution to a silver halide emulsion as described, for example, in JP-B-49-44895; and (4) mechanically dispersing a substantially water-insoluble photographic additive or additives in an aqueous system, and adding the dispersion of the photographic additives to a silver halide emulsion as described, for example, in JP-A-52-110012, JP-A-53-102733 and U.S. Pat. No. 4,006,025.
However, conventional process (1) above requires an organic solvent in an amount at least equal to the solubility of the additives. Hence, when using photographic additives which are only slightly soluble in the organic solvent, a large amount of organic solvent must be used to dissolve the additives, which causes the formation of agglomerates upon addition of the solution or dispersion thereby obtained to the emulsion or causes coating defects such as seediness or streaks.
Conventional process (2) above causes a change in concentration or decomposition of the photographic additives in the step of removing the organic solvent (by evaporation or membrane saparation), thus requiring complicated production steps.
In conventional process (3) above, wherein a solution solubilized by a surface active agent is added to a silver halide emulsion, emulsified particles existing in the silver halide emulsion are destroyed. Additionally, coating becomes increasingly difficult as the coating speed of a silver halide emulsion is accelerated, and the adhesiveness of the resulting silver halide light-sensitive materials is deteriorated.
In conventional process (4) above, the desired effects of the additives are reduced, and coating defects arise due to formation of precipitates, etc.
Further, a conventional process of adding an organic solvent solution of photographic additives to water or an aqueous solution containing an anionic surface active agent results in recrystallization upon addition. With some additives, the recrystallized crystals are not dispersible, but remain as coarse crystals of size 20 to 50 .mu.m which, when added to a silver halide, require a long time for such photographic additives such as spectral sensitizing agents to adsorb onto the silver halide grains and the additives thus fail to provide the desired photographic properties. Moreover, such emulsions are liable to cause coating defects due to the formation of precipitates, etc.
In a conventional process of adding a solution of a photographic additive or additives in an organic solvent to an aqueous solution containing an aqueous binder or a hydrophilic colloid, the dispersing efficiency is good due to the high viscosity of the aqueous binder solution or hydrophilic colloid in spite of the recrystallization. Recrystallization takes place upon addition of the solution, as described above. Extensive foaming occurs upon dispersion due to the large input power required for dispersion. The coarse crystals become enveloped in the foam and remain as such to similarly cause coating defects.